This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Hypothesis: This study is a multicenter, open-label study designed to assess the efficacy of risperidone in reducing irritability and associated behaviors displayed by children and adolescents who fulfill DSM-IV and Autism Diagnostic Interview (ADI) criteria. Although behavioral and educational therapies and a variety of medications may help manage some symptoms of autism, there are no FDA-approved treatments for the disorder. However, atypical antipsychotics have emerged as promising therapies for the behavioral symptoms of Autistic Disorder. Risperidone, the most rigorously studied of the atypical antipsychotics, is effective for serious behavioral problems in Autistic Disorder as it has potent effects on the dopamine and 5-HT neuronal systems, both of which have been implicated in the pathophysiology of autism